Control valves (e.g., sliding stem valves, rotary valves, axial flow valves, globe valves, etc.) are commonly used in industrial processes (e.g., oil and gas pipeline distribution systems and chemical processing plants) to control the flow of process fluids. To control fluid flow, a control valve often employs a flow control member (e.g., a plate, a disk, a plug, etc.) that moves relative to a valve seat positioned in a valve body of the control valve. For example, a control valve having a relatively tight shut-off capability provides shut-off control such that substantially no fluid flows through the control valve when the flow control member sealingly engages the valve seat. Fluid flow may be allowed and/or increased as the flow control member moves and/or rotates away from the valve seat.
Some known control valves employ a seal as part of the valve seat and/or the control flow member (e.g., along a peripheral edge of the flow control member) to effect and/or improve a seal between the flow control member and the valve seat. Typically, industrial process conditions, such as pressure conditions, operation temperatures, and the type of process fluids dictate the type of seals that may be used. For example, soft seals composed of elastomers (e.g., EPDM) or fluoropolymers (e.g., PTFE) allow the flow control member to engage the valve seat more tightly and, thus, provide improved sealing characteristics to help prevent or restrict fluid flow through the control valve (i.e., provide relatively tight shut-off or seal characteristics). However, soft seals composed of elastomers or fluoropolymers have lower temperature and/or erosion resistance characteristics compared to, for example, seals composed of metal. For example, some soft seals may become damaged when used with process fluids having temperatures greater than 600° F. and/or may erode when used with process fluids having significant fluid pressures or velocities. Thus, such known seals can be used in a limited temperature range and/or with flows having a limited pressure or velocity range.
Seals composed of metal, on the other hand, provide greater resistance to temperature and erosion compared to soft seals. While such known metal seals have greater resistance to high temperatures and erosion, such known metal seals provide inferior sealing capabilities compared to soft seals and, thus, metal seals may not meet desired shut-off capability and/or classification. In some applications, control valves employ a laminated seal composed of graphite and stainless steel. Although such known laminated graphite seals enable a relatively tight shut-off over a wide temperature range, portions of the graphite layers that remain exposed to the process fluids having relatively high pressures or velocities may be susceptible to erosion.